An Air Turbine Starter (ATS) is utilized to initiate Main Engine Start (MES) of a gas turbine engine. The ATS is commonly implemented as a Line Replaceable Unit (LRU) installed on the Accessory Gearbox (AGB) of the engine. By common design, an ATS includes a lubrication system, which maintains the rotating components of the ATS in a lubricated state during operation of the ATS. The lubrication system can be self-contained such that the ATS does not exchange oil with the larger gas turbine engine. Alternatively, the ATS may have a “shared oil” lubrication system enabling circulation of the engine oil through the ATS. The engine oil is typically conditioned (e.g., filtered, pressurized, and/or cooled) and thus maintained at a relatively high quality during the lifespan of the engine. Thus, by allowing the ATS to take advantage of this high quality oil supply, a shared oil lubrication system can prolong the service life and improve the overall reliability of the ATS.
While providing the above-noted benefits, equipping an ATS with a shared lubrication system also presents certain challenges. For example, in the unlikely event of an ATS housing breach (that is, a compromise in the sealed environment of the ATS), the engine oil circulated through the ATS can rapidly escape to the surrounding environment as liquid or vapor (oil trapped in air) due to the pressure differential between the ATS housing and its surrounding environment. If a significant volume of engine oil is lost through the ATS, inflight shutdown of the gas turbine engine may be necessitated. To help reduce the loss of engine oil through the ATS in the event of a housing breach, the ATS may be further equipped with an oil feed shutoff valve. The oil feed shutoff valve may typically reside in an open position under normal operational conditions. However, if an ATS housing breach should occur, the oil feed shutoff valve closes to impede the flow of engine oil into the ATS thereby effectively sequestering the leak and preventing significant oil loss through the ATS.
While serving as a useful oil loss control feature in the context of a shared oil ATS, conventional oil feed shutoff valves remain limited in certain respects. For example, as conventionally proposed, an oil feed shutoff valve may not provide a complete seal when closed. As a result, engine oil may still be permitted to flow into the ATS and escape to the external environment (e.g., the interior of nacelle) in the event of an ATS housing breach. Furthermore, even when equipped with an oil feed shutoff valve, a conventional ATS may lack an effective means for relieving the accumulation of oil pressure behind the shutoff valve when closed. As a result, undesired pressure build-up or “dead heading” of the engine oil may occur upstream of the shutoff valve further exacerbating oil leakage into the ATS under breach conditions. Finally, as a still further limitation, conventional ATS designs may permit undesired oil drainage back the AGB when the oil feed shutoff valve is in a fully or partially open position.
It is thus desirable to provide embodiments of a shared oil ATS including an oil feed shutoff valve, which overcomes one or more of the above-mentioned limitations. For example, it is desirable to provide a shared oil ATS having an oil feed shutoff valve, which achieves a high integrity seal when in a closed position to greatly reduce, if not entirely prevent the inflow of engine oil into the ATS under breach conditions. It is also desirable for such an ATS to alleviate the accumulation of oil pressure upstream of the shutoff valve when closed; and/or to prevent the undesired drainage of oil when the shutoff valve is in an open or partially open position. Finally, it is desirable to provide embodiments of a gas turbine engine including an ATS providing such performance characteristics. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.